Infrared lasers are used in various industrial applications to perform operations on substrates such as metal. Such operations include cutting a monolithic substrate into two or more pieces, or welding a substrate consisting of multiple pieces together.
The design of most laser beam delivery systems used in such industrial applications provides for the delivery of a powerful infrared laser beam to a target point on the substrate with precise focus and position. In addition, a pilot laser, which typically emits light in a range visible to the human eye and at an intensity that does not affect the substrate, is usually integrated into the laser beam delivery system as an indicator for the operator as to where the infrared laser will appear on the substrate. The pilot laser, in general, is a red laser with a wavelength range in the visible spectrum between 620 nm to 690 nm.
The main infrared laser beam enters the laser beam delivery system from a laser fiber cable via a beam delivery connector and is projected onto a target point by the laser beam delivery system optics, that is, the internal optics of the laser beam delivery system. The laser beam delivery system optics typically include a combination of specialized optical mirrors, lenses, filters and other optical devices that provide a focused, directed light beam of a specific wavelength. Typically the laser beam delivery system is designed to suit the type of welding to be performed. The same connector is also used for delivery of the pilot laser source through the laser beam delivery system optics.
On many laser beam delivery systems, a video camera port is included to allow for the optical coupling of a video camera to the system to allow the operator to visually observe the setup of the welding process (including material alignment and location) prior to activating the laser that will operate on the substrate. In such systems, the laser beam delivery system optics, that is, the internal optics of the laser beam delivery system, are configured, typically by way of a beam splitter, to direct light reflected from the substrate to the camera port. The camera port may take the form of a transparent window in a housing of the laser beam delivery system.
Typically, conventional video cameras are coupled to the camera port of a laser beam delivery system. They provide an adequate image of the work area through the laser beam delivery system optics prior to activating the laser that will operate on the substrate, and allows use of the pilot laser for initial positioning. However, once the operating laser is activated, it provides too much illumination and conventional video cameras become saturated with light, seriously inhibiting their ability to monitor operations on the substrate. Stated another way, because conventional video cameras have a low dynamic range, they cannot be effectively used during infrared laser welding or cutting processes as the image is too bright for the camera.
It is also known to use high dynamic range (HDR) cameras in welding operations. The term “dynamic range” refers to the ratio between the largest and smallest values that a signal (e.g. a light signal) may assume, and in base-10 is measured in decibel (dB). The term “high dynamic range” or “HDR”, as used herein, means an imaging capability of a dynamic range of at least 140 dB. Specialized HDR camera systems for welding operations include those offered by Xiris Automation Inc. having an address at 1016 Sutton Drive, Unit C5, Burlington, Ontario, Canada L7L 6B8. HDR cameras offer a good image when the operating laser (e.g. the infrared laser used to operate on the substrate) is active.
Thus, a logical solution for the problem of light saturation of conventional video cameras during infrared welding operations would seem to be replacement of the conventional video camera with an HDR video camera to be able to see the laser spot and substrate during operation of the infrared laser. Unfortunately, this merely substitutes one problem for another. While an HDR video camera provides very good imaging when the operating laser is active, when the operating laser is not active, there is insufficient light for the HDR video camera to effectively resolve the work surface.
One option that has been explored in an effort to resolve this latter problem is to use a co-axial illuminator in conjunction with an HDR video camera to illuminate the work surface with enough light to be seen by the HDR camera through the laser beam delivery system optics. In reality, however, because the optical components and specialized optical coatings of the laser beam delivery system optics are optimized for the delivery of the powerful operating infrared laser beam, there is substantial back reflection or “ghosting” in the optical path that results from the co-axial illumination light and from the pilot laser. This ghosting appears in the view seen by the HDR video camera, substantially impeding its effectiveness.
Thus, one was left with the dichotomous choice of either effectively observing the substrate before activation of the operating laser, or during the welding or cutting operation, but not both.